I have not heard of this term or any research dealing with using caffeine for anything other than astimulant..... I use & depend on Gibberellins (GibberellicAcid) for this purpose. and it does have limited use for the average propagator....

I've never heard of a caffeine soak.
But have heard that a weak tea solution helps soften the outside of the seed for quicker germination.. and if sprinkled on the ground, helps keep the soil from getting a hard crust, which happens alot here.

I think it was in my Jerry Baker books, but mom has them at the moment, so can't go look..

JoJo

I Looked up a research article from Cambridge University that says that caffeine actually inhibits germination of seeds and at very low dilutions shows no effect at all. So I would say be suspicious of any miracle treatments for seeds unless the idea can be independantly confirmed.